Sound transmission devices have advanced filtering abilities that theoretically protect the ear from harmful Masking noise while amplifying the sounds that need to be heard, such as backup alarms. Therefore, such devices should provide improved signal detection in noise when compared to their passive counterparts. The masked threshold of a vehicular backup alarm was determined for audiometrically normal and non-normal hearers using two types of sound transmission devices and their passive counterparts within pink noise and milling machine noise at intensities of 75, 85, 95 and 105 dBA. Results indicated that the sound transmission devices did not have any statistically significant advantages over the passive devices with respect to masked threshold of a backup alarm. Therefore, it cannot be concluded that these devices offer advantage over similar passive devices with respect to signal detection. Additionally, ratings of comfort and the ability to detect the alarm for each device were gathered. Both scales did not show any significant differences between the two device types.